I-line photoresist compositions

ABSTRACT

Negative photoimageable compositions are disclosed which contain a radiation sensitive component for producing an acid when subjected to radiation at wavelengths of 320 to 420 nanometers, a resin binder and a reactive oligomer. The compositions are useful in constructing printed circuits and integrated circuit packages.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to i-line photoresist compositions for printedcircuit applications which are imageable by exposure at i-linewavelengths of about 320 to 420 nanometers. In particular this inventionis directed to a photoresist composition that will unexpectedly reduceline growth of the resist image of the printed circuit and unexpectedlyhas a longer shelf (storage) life than would have been expected.

2. Description of the Art

Photoresists are photosensitive films used to transfer images to asubstrate. They are applied as liquid coatings or dry film compositionsto a substrate to provide a photosensitive resist article. After formingthe film on the substrate, the film is exposed through a patternedphotomask to a source of activating energy such as light to form alatent image thereon after development. The photomask has areas opaqueto activating radiation and other areas transparent to activatingradiation. The pattern in the photomask of opaque and transparent areasdefines a desired image that may be used to transfer the image to asubstrate. A relief image is provided by development of the latent imagepattern in the resist coating. The use of photoresist coatings isgenerally described, for example, by DeForest, Photoresist Materials andProcesses, McGraw Hill book Company, New York (1975), and by Moreau,Semiconductor Lithography, Principals, Practices and Materials, PlenumPress, New York (1988) as well as in U.S. Pat. No. 5,366,846, the entirecontents of this patent are incorporated herein by reference hereto.While the teachings of the above mentioned U.S. Pat. No. 5,366,846 arequite significant, it has been found that after development of theimaged photoresists, line growth of the resist had occurred. Therefore,there is still a need for better sidewall definition without substantialline growth during processing. The composition of the present inventionprovides a composition that even further reduces line growth of theresist sidewalls during development. Line growth produces etched lineswhich do not properly reproduce the desired geometries as defined by themask.

Reference should also be had to the following for a greaterunderstanding of the art: U.S. Pat. Nos. 5,034,304; 5,128,232;4,189,323, 3,954,475, 5,057,397, 5,340,697, 4,826,753, 5,180,653,5,340,697, and the following patents or publications: Canadian PatentNo. 2100,392, Japan 63075737A2, Japan 05,303,196; 05,281,727 andEuropean Patent Application Nos. 0 458 325, 0 519 298, 0 621,509, 0483,689, 0 483,693 and 0,672,954.

SUMMARY OF THE INVENTION

The present invention provides novel radiation sensitive coatingcompositions that are characterized in part as providing a cured coatinglayer that exhibits substantial flexibility as well as reducing linegrowth thereof during processing after a photoimaging step. In general,a composition of the invention comprises a resin binder, a reactiveoligomer that comprises one or more internal crosslinking groups, and aradiation sensitive component (photoacid generator) that isphotoactivatable at a wavelength of from about 320 to 420 nanometers.Such materials may be a substituted triazine compound or a substitutedoxadiazole compound which produces an acid when activated by lightenergy at the wavelengths set forth above. As used herein, the term"reactive oligomer" refers to a material that is a polymer moleculecontaining a number of repeating units, e.g., 2 to 50 and that iscrosslinkable when in contact with photogenerated acid such as providedby triazines and oxadiazoles. Such reactive oligomers include materialssuch as the epoxidized butadiene family (See U.S. Pat. No. 5,366,846incorporated herein by reference hereto), acetals, vinyl ethers andothers as would be clear to those skilled in the art after reading thisapplication.

While substantially non-reactive resin binders are suitably employed inthe compositions of the invention, preferably the resin binder is areactive polymer that can undergo photoactivated crosslinking with oneor more components of the composition.

A variety of resin binders can be employed. Suitable reactive resins arethose that contain a functional group that can react with one or moreother components of the composition, for example a reactive hydrogencontaining resin. Generally preferred reactive resins are phenolicresins. With respect to the crosslinker component, a variety ofcrosslinking agents may be employed. Preferred crosslinkers include anepoxy-containing materials and amine-based crosslinkers such asmelamines, ureas, guanamines and mixtures thereof. Such crosslinkerswill cure to form a polymerized network with the resin binder andreactive oligomer. Compositions of the invention are suitable for use asa liquid coating composition as well as a dry film.

The compositions of the invention have utility in a variety ofapplications. Hence, the invention includes processes employing thecompositions of the invention, including processes for forming a reliefimage, processes for forming an imaged dielectric layer on a substrate,and processes for the manufacture of printed circuit boards, additiveprinted circuits, multilayer printed circuits, high density printedcircuits, flexible circuits, surface mount devices, multichip modules,sequential build and other articles. The invention further providesnovel articles of manufacture comprising substrates coated with thecompositions of the invention.

The terms "crosslink", "crosslinking" and other such terms used hereinrefer to any reaction of one or more of the components of a compositionof the invention that results in reduced developer solubility of thecomposition.

Products such as these above are first photochemically set, the unwantedareas removed, and the remaining organic material is thermally fullyset, i.e., hardened to its ultimate state.

DETAILED DESCRIPTION OF THE INVENTION

A composition of the invention in general comprises a resin binder, anacid sensitive crosslinkable oligomer and a radiation activatedcomponent which produces an acid after radiation is directed thereon atwavelengths between about 320 to 420 nanometers. Preferably thecompositions further include a crosslinking agent component in additionto the reactive oligomer.

The resin binder component may comprise a nonreactive resin or,preferably, the resin binder is a reactive resin that can undergophotoinitiated crosslinking with one or more components of thecomposition either photochemically or thermally. The resin binderpreferably imparts aqueous alkaline developability to the composition.Thus, preferred resin binders include resins that contain polarfunctional groups, such as hydroxyl or carboxylate, that can impartaqueous alkaline developability. Further, the resin binder component ispreferably employed in a composition in a concentration sufficient torender unexposed portions of a coating layer of the composition aqueousalkaline developable.

The term "nonreactive resin" as used herein refers to a resin that doesnot substantially polymerize with one or more of the components of thecomposition upon photoactivation of the same. Thus, upon curing of acomposition, a nonreactive resin binder typically will be encapsulatedwithin the polymerizable component(s) of the composition. Suitablenonreactive resins include, for example, urethanes, silicones, acrylatesand the like. The resin binder component suitably may comprise bothnonreactive and reactive resin binders.

A reactive resin binder is suitably any of a variety of materials thatwill undergo photoinitiated crosslinking with one or more components othe composition. Thus suitable resins include those that contain one ormore reactive moieties, for example a functionality that contains areactive hydrogen. Phenolic resins are particularly suitable reactiveresins and are preferably employed in a concentration sufficient torender a coating layer of the composition developable with an aqueousalkaline solution or semi-aqueous alkaline solution. Suitable phenolicresins include, for example, phenol aldehyde condensates known in theart as the novolak resins, homo and copolymers of alkenyl phenols,partially hydrogenated novolak and poly(vinylphenol) resins, and homoand copolymers of N-hydroxyphenyl-maleimides.

Of the phenolic resins suitable as a reactive resin for the compositionsof the invention, the phenol formaldehyde novolaks are preferredmaterials as the novolaks are able to form an aqueous alkalinedevelopable, photoimageable coating composition. These resins are madefollowing procedures known and disclosed in numerous publications suchas DeForest, Photoresist Materials and Processes, McGraw-Hill BookCompany, New York, Ch. 2, 1975; Moreau, Semiconductor LithographyPrinciples, Practices and Materials, Plenum Press, New York, Chs. 2 and4, 1988; and Knop and Pilato, Phenolic Resins, Springer-Verlag, 1985,all said publications incorporated herein by reference for theirteaching of making and using novolaks and other phenolic resins.

More particularly, novolak resins are the thermoplastic condensationproduct of a phenol and an aldehyde. Examples of suitable phenols forcondensation with an aldehyde, especially formaldehyde, for theformation of novolak resins, include phenol; m-cresol; o-cresol;p-cresol; 2,4-xylenol; 2,5-xylenol; 3,4-xylenol; 3,5-xylenol; thymol andmixtures thereof. An acid catalyzed condensation reaction results in theformation of a suitable novolak resin which may vary in molecular weightfrom about 500 to 100,000 daltons. Preferred novolak resins include thecresol formaldehyde condensation products.

Another preferred reactive resin is a poly(vinylphenol) resin.Poly(vinylphenols) are thermoplastic materials that may be formed byblock polymerization, emulsion polymerization or solution polymerizationof corresponding monomers in the presence of a cationic catalyst.Vinylphenols used for production of poly(vinylphenol) resins may beprepared, for example, by hydrolysis of commercially available coumarinsor substituted coumarins, followed by decarboxylation of the resultinghydroxy cinnamic acids. Useful vinyl phenols may also be prepared bydehydration of the corresponding hydroxyalkyl phenol or bydecarboxylation of hydroxy cinnamic acids resulting from the reaction ofsubstituted or non-substituted hydroxy benzaldehydes with malonic acid.Preferred poly(vinylphenol) resins prepared from such vinyl phenols havea molecular weight range of from about 2,000 to about 100,000 daltons.Procedures for the formation of poly(vinylphenol) resins also can befound in U.S. Pat. No. 4,439,516 incorporated herein by reference.

Other suitable reactive resin are polymers containing phenolic units andnonaromatic cyclic alcohol unites analogous in structure to the novolakresins and poly(vinylphenol) resins. Such copolymer resins are describedin European Published Patent Application No. 0 401 499 having apublication date of Dec. 12, 1990 and incorporated herein by reference.

An additional class of suitable phenolic reactive resins include homoand copolymers of N-hydroxyphenyl maleimides. Such materials aredisclosed in European Published Appln. No. 0,255,989 beginning on page2, line 45 and continuing to page 5, line 51, incorporated herein byreference.

The concentration of the resin component of the compositions of theinvention may vary within relatively broad ranges, and in general theresin component is between about 30 and 60 or more weight percent oftotal solids of the compositions. In general a reactive resin isemployed in a composition in a concentration of from about 0 (where onlynonreactive resin(s) are employed) to 60 or more weight percent of thetotal solids of the composition. As used herein, the term total solidsof a composition refers to all components of a composition other than asolvent carrier.

Another component of the compositions of the invention is preferably areactive oligomer such as an epoxidized polybutadiene that comprises oneor more internal epoxide groups. The epoxidized polybutadiene suitablymay also contain reactive groups in addition to one or more internalepoxy functionalities. For example, the butadiene may contain one ormore vinyl groups, hydroxyl groups, carboxyl groups or pendant and/orterminal epoxy groups.

Particularly preferred epoxidized polybutadienes of the compositions ofthe invention are represented by the following formula (I): ##STR1##where R and R¹ are each independently selected from the group consistingof hydrogen, substituted and unsubstituted alkyl, substituted andunsubstituted aryl and a reactive group such as hydroxy, epoxy or analkylene group, for example an alkylene group having from 2 to 10 carbonatoms, more typically having 2 carbon atoms. Suitable alkyl groupsinclude those having from 1 to about 10 carbon atoms more typically from1 to about 6 carbon atoms. Phenyl is a suitable aryl group. The alkyland aryl groups may be suitably substituted by, for example, aryl,alkyl, alkylene, halo, alkoxy or hydroxy. The group R² of formula (1) ispreferably an alkylene carbon that forms a vinyl group with the carbonpendant to the butadiene backbone (i.e., R² is CH₂ ═), although apolybutadiene of formula (I) can be modified so that for one or moreunits of the butadiene the group R² is other than an alkylene carbon.For example such an alkylene group can be saturated so that R² is analkyl carbon such as methyl. The value n of the above formula (I) issuitably 2 or greater, more preferably n is a value between about 10 and25, still more preferably n is a value between about 20 and 25.

The polybutadiene of formula (I) above preferably has a molecular weight(weight average) of at least about 4000, preferably has a molecularweight of between about 4000 and 8000, still more preferably has amolecular weight between about 5000 and 6000.

A polybutadiene of formula (I) can be prepared in several ways. Forexample, a commercially available polybutadiene can be selectivelyoxidized to provide internal epoxide groups. Typicallypoly-1,3-butadienes are employed. Polybutadienes, includingpolybutadiene that with varying terminal groups including reactivegroups such as hydroxy, are available from vendors such as BF Goodrich,Nisso and Japan Synthetic Rubber. Under appropriate reaction conditions,an internal alkylene group will be more reactive to electrophilicsubstitution than a pendant vinyl group (i.e., where R² above is analkylene carbon). Thus, an internal carbon-carbon double bond of thepolybutadiene can be converted to a halohydrin by reaction with ahalogen such as Cl₂ or Br₂ in the presence of water and a substantiallynon-nucleophilic solvent such as tetrahydrofuran or an aromatic solventsuch as toluene or xylene. The epoxide can then be formed by alkalinetreatment of the halohydrin. Suitable bases for formation of theinternal epoxide via a halohydrin include alkoxides such as potassiumt-butoxide and hydroxides such as sodium hydroxide. In formation of thehalohydrin, a stoichiometric equivalent of halogen should be employed tolimit addition to the more reactive disubstituted internal vinyl groupsof the polybutadiene.

It is also believed that direct oxidation of the internal alkylene groupof the polybutadiene can be employed to form a epoxidized polybutadieneof the invention. For example, a commercially available polybutadienecan be admixed in a suitable solvent and reacted with a suitable oxidantto provide the epoxide group. Suitable oxidants will include peracidssuch as perbenzoic acid, meta-chlorobenzoic acid, peracetic acid andtrifluoroperacetic acid; alkaline oxidants such as sodium hydroxide andhydrogen peroxide (30 wt. % in water); or a substantially neutraloxidation of bubbling O₂ gas though the reaction mixture in the presenceof a suitable catalyst such as Ag.

The internally epoxidized polybutadiene is preferably miscible withother components(s) of the composition both before and after curing. Anepoxidized polybutadiene that is miscible with other components uponcuring is believed to form a clear coating layer upon curing of thecomposition while a butadiene that is not miscible will provide anopaque cured coating layer, for example a milky-colored coating layer.While not wishing to be bound by theory, it is believed a clear, curedcoating layer indicates the formation of a polymerized networkcomprising a substantially uniform distribution of the polymerizablecomponents of the composition.

The concentration of the internally epoxidized butadiene component mayvary within relatively broad ranges, and in general the internallyepoxidized polybutadiene is employed in a concentration of at leastabout 10 weight percent of the total solids of a composition, moretypically from about 10 to 60 or more weight percent of the totalsolids, still more typically from about 25 to 55 weight percent of totalsolids of a composition.

The compositions of the invention further includes radiationpolyvinylphenol resin having a minor portion of its hydroxyl groupsmesylated admixed with a novolak resin.

In addition to the resin and epoxidized polybutadiene componentsdescribed above the photoresist contains a photoacid producing compoundwhich undergoes photolysis with activating radiation at a wavelength ofabout 320 to 420 nanometers to yield a strong halogen acid. Suitableacid producing compounds halomethyl-s-triazines which conform to thefollowing formulae II: ##STR2## where P is a substituted orunsubstituted phenyl group or a substituted or unsubstituted naphthylgroup and each X may be the same or different and each represents ahalogen atom, preferably Cl or Br. Preferably P is the group: ##STR3##when X is Cl or Br.

A preferred halomethyl-s-triazine conforms to the following formula m:##STR4## wherein Q is bromine or chlorine, P is NHR, --NR₂, or --ORwhere R is phenyl or lower alkyl (lower alkyl meaning an alkyl grouphaving 6 carbon atoms); n is an integer from 1 to 3; and W is anoptionally substituted aromatic or heterocyclic nucleus or the compoundof formula IV: ##STR5## where Z is oxygen or sulfur and R¹ is hydrogen,a lower alkyl or phenyl group. Of course, where W is an aromatic orheterocyclic nucleus, the ring may be optionally substituted. Withoutattempting an exhaustive listing of substituents, the following arenoted as typical: chloro, bromo, phenyl, lower alkyl (an alkyl having nomore than 6 carbon atoms), nitro phenoxy, alkoxy, acetoxy, acetyl, aminoand alkyl amino.

The s-triazine compounds as described above generate free radicals whenirradiated with actinic radiation of a wavelength from about 320 toabout 420 nanometers. For this reason, the compounds are useful asphotoinitiators in light sensitive compositions herein within the i-linewavelengths.

The s-triazine compounds are condensation reaction products of certainmethyl-halomethyl-s-triazines and certain aldehydes or aldehydederivatives. They may be prepared by the procedures disclosed in theabove cited U.S. Pat. No. 3,954,475 and in accordance with the teachingsof Wakabayashi et al., Bulletin of the Chemical Society of Japan, 42,2924-30 (1969).

Specific examples of halogenated triazines suitable for use as photoacidgenerators in the invention include for example, 2-1-(3,4-benzodioxolyl)!-4,6-bis(trichloromethyl)-1,2,5-triazine, 2-1-(2,3-benzodioxolyl)!-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-1-(3,4-benzodioxolyl)!-4,6-bis(tribromomethyl)-1,3,5-triazine, 2-1-(2,3-benzodioxolyl)!-4,6-bis(tribromomethyl)-1,3,5-triazine,2-(2-furfylethylidene)-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-2-(5-methylfuryl)ethylidene!-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-2-(4-methylfuryl)ethylidene!-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-2-(3-methylfuryl)ethylidene!4,6-bis-(trichloromethyl)-1,3,5-triazine, 2-2-(4,5-dimethylfuryl)ethylidene!-4,6-bis(trichloromethyl)-1,3,5-triazine,2-2-(5-methoxyfuryl)ethylidene!-4,6-bis(trichloromethyl)-1,3,5-triazine,2-2-(4-methoxyfuryl)ethylidene!-4,6-bis(trichloromethyl)-1,3,5-triazine,2- 2-(3-methoxyfuryl)ethylidene!-4,6-bis(trichloromethyl)-1,3,5-triazine, 2-2-(4,5-dimethoxy-furyl)ethylidene!-4,6-bis(trichloromethyl)-1,3,5-triazine,2-(2-furfylethylidene)-4,6-bis(tribromomethyl)-1,3,5-triazine, 2-2-(5-methylfuryl)ethylidene!-4,6-bis(tribromomethyl)j-1,3,5-triazine, 2-2-(4-methylfuryl)-ethylidene!-4,6-bis(tribromomethyl)-1,3,5-triazine, 2-2-(3-methylfuryl)ethylidene!-4,6-bis(tribromomethyl)-1,3,5-triazine, 2-2-(4,5-dimethoxyfuryl)ethylidene!-4,6-bis(tribromomethyl)-1,3,5-triazine,2- 2-(5-methoxyfuryl)ethylidene!-4,6-bis(tribromomethyl)-1,3,5-triazine,2- 2-(4-methoxyfuryl)ethylidene!-4,6-bis(tribromomethyl)-1,3,5-triazine, 2-2-(3-methoxyfuryl)ethylidene!-4,6-bis(tribromomethyl)-1,3,5-triazine, 2-2-(4,5-dimethoxyfuryl)ethylidene!-4,6-bis(tribromomethyl)-1,3,5-triazine,2,4,6-tris-(trichloromethyl)-1,3,5-triazine,2,4,6-tris-(tribromomethyl)-1,3,5-triazine,2-phenyl-4,6-bis(trichloromethyl)-1,3,5-triazine,2-phenyl-4,6-bis(tribromomethyl)-1,3,5-triazine,2-(4-methoxyphenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,2-(4-methoxyphenyl)-4,6-bis(tribromomethyl)-1,3,5-triazine,2-(1-naphthyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,2-(1-naphthyl)-4,6-bis(tribromomethyl)-1,3,5-triazine,2-(4-methoxy-1-naphthyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,2-(4-methoxy-1-naphthyl)-4,6-bis(tribromomethyl)-1,3,5-triazine,2-(4-chlorophenyl)-4,6-bis(tribromomethyl)-1,3,5-triazine,2-styryl-4,6-bis(trichloromethyl)-1,3,5-triazine,2-styryl-4,6-bis(tribromomethyl)-1,3,5-triazine,2-(4-methoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,2-(4-methoxystyryl)-4,6-bis(tribromomethyl)-1,3,5-triazine,2-(3,4,5-trimethoxystyryl)-4,6-bis(trichloromethyl)-1,3,5-triazine,2-(3,4,5-trimethoxystyryl)-4,6-bis(tribromomethyl)-1,3,5-triazine,2-(3-chloro-1-phenyl)-4,6-bis(trichloromethyl)-1,3,5-triazine,2-(3-chlorophenyl)-4,6-bis(tribromomethyl)-1,3,5-triazine and the like.

Other photoacid generator activated at 320 to 420 nanometers suitablefor use in this invention include substantial oxadiazols of the formulaV ##STR6## where X is Cl or Br and in particular where X is Cl.

Other triazine type photoacid producers that may be used for i-lineexposure are disclosed in EP application 0,458,325 and taught in U.S.Pat. No. 5,366,846.

The acid-generating agents compounds disclosed herein may be used aloneor in admixture. The amount of acid generator may vary from about 0.01to 5 parts by weight, preferably 0.1 to 3 parts by weight, per 100 partsby weight of the specific alkali soluble resin. When the amount of theacid-generator is less than 0.01 parts by weight, it is difficult toform a resist pattern and when the amount exceeds 5 parts by weight, theability to strip the resist from the substrate becomes difficult.

In addition to the above a spectral photosensitizer component may alsobe included in the negative photoresist composition.

The preferred spectral photosensitizers are anthracene or substitutedanthracene compounds such as diphenylanthracene, phenanthracenethioxanthones such as isopropyl thioxanthones of the structure: ##STR7##

A compound that contains at least two vinyl ether groups is a suitablecrosslinker for compositions that comprise a photoacid generatorcompound as disclosed herein. Examples of compounds with at least twovinyl ether groups include divinyl ethers of aliphatic, cycloaliphatic,aromatic or araliphatic diols. Examples of such materials includedivinyl ethers of aliphatic diols having from 1 to 12 carbon atoms,polyethylene glycols, propylene glycols, polybutylene glycols,dimethylcyclohexanes, etc. Specific examples include divinyl ethers ofethylene glycol, trimethylene-1,3-diol, diethylene glycol, triethyleneglycol, dipropylene glycol, tripropylene glycol, resorcinol, BisphenolA, etc. A composition of the invention may also suitably comprise amelamine as a crosslinker or a composition may contain two or moredifferent crosslinkers.

The concentration of the one or more crosslinkers in a composition mayvary within a relatively wide range. As will be appreciated to thoseskilled in the art, suitable concnetrations will vary with factors suchas crosslinker reactivity and specific application of the composition.In general, a suitable concentration of one or more crosslinkers isabout 5 to 30 weight percent of total solids of the composition,preferably about 10 to 20 weight percent of total solids.

Other additives may be optionally included in the compositions of theinvention such as dyes, fillers, wetting agents, fire retardants and thelike. A suitable filler is the product sold under the name TALC byCyprus Chemical and a suitable dye is Orasol Blue available from CibaGeigy.

Thermal curing after development may be conducted at temperaturesranging from about 120° to 180° C., preferably 120° to 140° C., for aperiod of time between about 20 to 120 minutes. The thermal cure hardensunreacted components, promotes flexibility of the coating layer and canenhance adhesion of the coating layer to the substrate. The coatinglayer also may be post cured using RF or microwave energy by methodswell known in the coatings industry.

The compositions of the invention will be highly useful as flexiblephotoimageable cover coats in the manufacture of flexible circuits. Asuitable process for the manufacture of a flexible circuit provides foretching a flexible base material to form a circuit layer by standardprocedures (e.g., print and etch), stripping of photoresist, followed bycleaning of the base material surface. A composition of the invention isthen applied to the cleaned surface. The composition may be suitablyapplied to the base material by a variety of coating means, for exampleroller coating or screen coating. The applied coating layer is thenimaged and developed to provide openings, e.g., for solder pads. Thecoated base material can then be processed and used in accordance withknown procedures. For such flex circuit applications, the photoimageablecomposition preferably comprises a brominated phenolic resin binder toprovide a more fire retardant composition coating layer. As is clear tothose in the art, a brominated phenolic resin is a resin where at leasta portion of the resin phenolic units are bromo substituted at one ormore available ring positions.

Compositions of the invention will also be useful as dielectricinnerlayers for multilayer printed circuit boards that are produced by asequential layering process as described above and in U.S. Pat. No.4,902,610. For example, a composition of the invention can be coatedover a first circuit layer and then the coating layer imaged to provideopenings that define interconnections, and then one or more other boardlayers sequentially formed over the imaged composition layer to form acircuit board having two or more layers of circuitry. The first circuitlayer will be in electrical connection with other circuit layer(s) ofthe board by means of the imaged openings of the coating layer. Atypical application of a dielectric innerlayer would compriseapplication of a two mil layer of a photoimageably composition of theinvention over a pre-cleaned circuitry substrate having 6-mil wideconductors, formation of 3-mil diameter via apertures in the coatinglayer by means of exposure and developed as discussed above; andpost-development curing of the photodielectric layer. The via apertureswill be located at predetermined sites within the width of theunderlying conductors. Thus the apertures can be formed simultaneouslyrather than individually drilling holes as is done in conventionalmultilayer board manufacturing processes. Further, the apertures can besignificantly smaller in such a sequential fabrication process than canbe done by drilling. For example, photoformed via apertures can beprovided with diameters as small as 2-mil. Additionally, via aperturesof any shape can be imaged and developed, including squares and slots.The vias can then be plated with electroless copper at the same time asthe second layer of circuitry conductors are plated.

Other applications of the compositions of the invention include use asan outerlayer for surface pad mounts where, the pads interconnected tothe underlying circuit layer of a printed circuit board by means ofelectrolessly plated photoformed vias. The compositions of the inventioncan also be used as a resist in full-build additive plating processessuch as printed circuit manufacturing processes. For a full-buildadditive circuit manufacturing process, it is highly desirable to employa permanent photoimageable dielectric mask as insulation between theelectrolessly plated circuitry conductors. Further, the photoimageablemask should be capable of fine line resolution, aqueous developable andserve as a resist to full build high pH electroless copper platingsolutions for many hours at elevated temperatures without unwantedextraneous copper deposition on the mask.

The following non-limiting Examples are illustrative of the invention.

EXAMPLES 1 THROUGH 12

Four different photoimageable compositions of the invention wereprepared by admixing the components in the amounts as specified in thebelow Table. Amounts listed in the Table grid are expressed in parts byweight based on the total weight (including solvent) of the specifiedcomposition.

                  TABLE    ______________________________________                           Amount    Composi-               Epoxi-    tion of        Amount  dized        Amount                                              Amount    Example           Resin   Resin   Buta- Amount Divinyl                                              Acid    No.    Binder  Binder  diene Melamine                                        Ether Producer    ______________________________________    1      A       50      30    10     0     4    2      B       45      35    10     0     4    3      C       45      35    10     0     4    4      D       50      30    10     0     4    5      E       60      30    10     0     4    6      F       50      40    10     0     4    7      A       50      0     10     30    4    8      B       45      0     10     35    4    9      C       45      0     10     35    4    10     D       50      0     10     30    4    11     E       60      0     10     30    4    12     F       50      0     10     40    4    ______________________________________

In addition to the components listed in the above Table,2-ethyl-9,10-dimethoxyanthracene was employed as a photosensitizer ineach of the compositions at a concentration of 1 part by weight based onthe total weight of the specified composition.

The solvent used in each of the compositions was propylene glycolmonomethyl ether acetate. Each of the compositions was formulated atabout 42 percent by weight solids.

In the above Table, the following designations represent the followingmaterials:

Resin Binders:

A is a cresol-formaldehyde novolak having a molecular weight (weightaverage) of about 11,000.

B is a m-cresol-formaldehyde having a melting point of about 145-155°and a molecular weight (weight average) of about 5500.

C is a poly(vinylphenol) resin having a molecular weight (weightaverage) of about 5200.

D is a poly(vinylphenol) resin having a molecular weight (weightaverage) of about 13700.

E is a partially hydrogenated polyvinyl phenol resin containing phenolicand nonaromatic cyclic alcohol units and having a molecular weight(weight average) of about 5200.

F is a polyacrylate formed by free radical polymerization of thefollowing monomer mixture: about 12 parts by weight methacrylic acid, 8parts by weight hydroxyl-ethylmethyl acrylate, 40 parts by weight butylacrylate and 49 parts by weight methylmethacrylate.

The divinyl ethers may be selected from e.g., BDDVE, DVE-2, DVE-3,DVE-4, ESDVE, HDDVE, CHDVE, DVE-4, DES200-DVE and PTHF 290-DVEmanufactured by BSAF and ISP.

The epoxy butadiene used in the compositions was an epoxidizedpolybutadiene obtained from Atochem North America, Inc. (Philadelphia,Pa.) under the tradename Poly bd 605 Resin and was a compound of formula(1) as defined above where R and R¹ are both hydroxyl and R² is analkylene carbon that forms a pendant vinyl group. The polybutadiene hada molecular weight of about 5500 and an epoxy equivalent weight of about260.

The melamine used in the compositions was a melamine-formaldehyde resinavailable from American Cyanamid under the trade name Cymel 303.

The acid producer used in the compositions was the compound known asTriazine B of the formula: ##STR8##

EXAMPLE 13

Formation of Relief Images

Each of the compositions of Examples 1-4 above is separately applied byMeier rod to a dry film thickness of about 22 to 28 microns on thecopper surface of a one-sided copper-clad plastic laminate. Prior toapplication of a composition, the copper surface of the substrate isscrubbed clean with pumice-based Scrub Cleaner 28 (available fromShipley Company), followed by water rinsing and drying of the scrubbedcopper surface. The applied liquid coatings is dried for 30 minutes in a90° C. fresh air circulating convection oven. The coated parts is theneach exposed with a Mimir light source using a 250 mJ/cm² exposure dose,except for the part coated with the composition of Example 5 whichrequired a higher exposure dose. The compositions of each of Examples1-4 is subject to broad band exposure. Following exposure, the coatedparts is post exposure baked for 20 minutes at 90° C. After cooling, theexposed coating layers is immersion developed at about 30-35° C. withDeveloper 303A (aqueous sodium hydroxide developer available from theShipley Company). The developed coating layers is then cured at either135° C. or 160° C. for 60 minutes.

EXAMPLE 14

Adhesiveless copper-clad films of the polyimide sold under the tradenameKAPTON were etched to remove the copper. The composition of Example 1above is applied to the KAPTON film to provide film thicknesses of about20-25 microns. The coated films were exposed, developed and cured asdescribed in U.S. Pat. No. 5,340,697, Example 18 (incorporated herein byreference).

EXAMPLE 15

The compositions of Examples 2 and 3, are each coated onto separatecopper-clad plastic laminates and dried, exposed, enhancement baked,developed and cured by the procedures described in Example 18 of U.S.Pat. No. 5,340,697 (incorporated herein by reference). The curedcomposition layer is then cut in a cross hatch pattern with a razorblade.

EXAMPLE 16

Full-build additive plating

One ounce copper clad epoxy laminates substrates is etched to therebybare a roughened epoxy surface with micropores. The substrates is thenimmersed in the electroless catalyst solution CATAPOSIT 44 (availablefrom the Shipley Company) for five minutes followed by water rinsing anddrying of the treated substrates. By means of a #44 Meier rod, thecompositions of Example 3 is applied to separate catalyzed copper cladsubstrates, dried, image exposed, enhancement post exposure baked for 15minutes at 100° C., developed with 303A Developer (ShipleyCompany),rinsed, dried and cured for 60 minutes at 140° C. to provide1.1 mil deep trenches exposing the catalyzed epoxy in a circuitrypattern. The parts is then immersed in Accelerator 19A (available fromShipley Co.) for five minutes to accelerate the palladium/tin platingcatalyst, water rinsed, and is then placed in a full build electrolesscopper bath until a 1 mil thickness (about 25 microns) is deposited inthe noted trenches. The plating bath is operated at about 70° C. anddeposited copper at 2.2 microns per hour.

EXAMPLE 17

Each of the compositions as described in Examples 1 to 12 are coatedonto a polyester film such as MYLAR® brand polyester film, and dried.The dried composition is then covered with a polyethylene cover sheet toproduce a dry film photoresist useable as described in 13 to 16.

In use, the polyethylene sheet is removed and the photoresistcomposition is roll laminated to copper surface during the sequentialbuild passes. See for example, U.S. Pat. Nos. 4,992,354 and 5,213,945which disclose use of a dry film photoresist.

The foregoing description of the invention is merely illustrativethereof, and it is understood that variations and modifications can beeffected without departing from the scope or spirit of the inventions asset forth in the following claims.

I claim:
 1. An i-line negative photoimageable composition which isphotoimageable at a wavelength of about 320 to about 420 nanometers,said composition comprising in combination a photoacid generator whichis a an oxidiazole of the formula ##STR9## where X is selected from thegroup consisting of chlorine and bromine, a reactive oligomer thatcontains one or more crosslinking groups and a resin binder.
 2. Thecomposition of claim 1 in which X is Cl.
 3. The composition of claim 1in which X is Br.
 4. The composition of claim 1 where the compositionfurther includes a crosslinking agent.
 5. The composition of claim 4where the crosslinking agent is a compound that contains at least twovinyl ether groups.
 6. The composition of claim 1 where the oligomer isa compound of the following formula: ##STR10## where R and R¹ are eachindependently selected from the group consisting of hydrogen,substituted and unsubstituted alkyl, substituted and unsubstituted aryl,epoxy, hydroxy and alkylene; R² is selected from the group consisting ofalkylene and alkyl; and n is an integer equal to 2 or greater.
 7. Thecomposition of claim 1 where the oligomer is a compound of the followingformula: ##STR11## where n is an integer between about 10 and
 25. 8. Thecomposition of claim 1 where the resin binder is selected from the groupconsisting of (1) a novolak resin, (2) a poly(vinylphenol) resin, (3) aresin containing phenolic units and cyclic alcohol units; and (4) abrominated phenolic resin.
 9. The composition of claim 1 furthercomprising a photosensitizer.
 10. The composition of claim 1 where thecomposition is developable in an aqueous alkaline solution orsemiaqueous alkaline solution.